Datasheet for the 2N3553 provided as a 45.1 KB PDF and categorised as a schematic. The name states only the 2N part number, with no manufacturer, package or revision. Such a sheet gives the electrical characteristics and case drawing for this transistor, which a technician needs when checking a suspected failure, matching a replacement or confirming lead order before soldering. Open it in a PDF viewer and confirm that the vendor logo and package of the actual part correspond to the document.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @cyberlanelectonik. Enginerys does not host this file.
How to open a .pdf file
The standard format for schematics, block diagrams, power-sequence charts and service manuals.